Feature/add show stack (#5)

* add -s flag and show command to display the last 5 entries

calc.go

@@ -32,6 +32,7 @@ type Calc struct {
 	debug        bool
 	batch        bool
 	stdin        bool
+	showstack    bool
 	stack        *Stack
 	history      []string
 	completer    readline.AutoCompleter
@@ -48,6 +49,7 @@ type Calc struct {
 const Help string = `Available commands:
 batch                toggle batch mode
 debug                toggle debug output
+show                 show the last 5 items of the stack
 dump                 display the stack contents
 clear                clear the whole stack
 shift                remove the last element of the stack
@@ -81,7 +83,7 @@ median               median of all values`
 // commands, constants and operators,  defined here to feed completion
 // and our mode switch in Eval() dynamically
 const (
-	Commands  string = `dump reverse debug undebug clear batch shift undo help history manual exit quit swap`
+	Commands  string = `dump reverse debug undebug clear batch shift undo help history manual exit quit swap show`
 	Constants string = `Pi Phi Sqrt2 SqrtE SqrtPi SqrtPhi Ln2 Log2E Ln10 Log10E`
 )
 
@@ -162,14 +164,21 @@ func (c *Calc) ToggleStdin() {
 	c.stdin = !c.stdin
 }
 
+func (c *Calc) ToggleShow() {
+	c.showstack = !c.showstack
+}
+
 func (c *Calc) Prompt() string {
 	p := "\033[31m»\033[0m "
 	b := ""
+
 	if c.batch {
 		b = "->batch"
 	}
+
 	d := ""
 	v := ""
+
 	if c.debug {
 		d = "->debug"
 		v = fmt.Sprintf("/rev%d", c.stack.rev)
@@ -271,6 +280,8 @@ func (c *Calc) Eval(line string) {
 				for _, entry := range c.history {
 					fmt.Println(entry)
 				}
+			case "show":
+				c.ToggleShow()
 			case "exit":
 				fallthrough
 			case "quit":
@@ -282,6 +293,16 @@ func (c *Calc) Eval(line string) {
 			}
 		}
 	}
+
+	if c.showstack && !c.stdin {
+		dots := ""
+
+		if c.stack.Len() > 5 {
+			dots = "... "
+		}
+		last := c.stack.Last(5)
+		fmt.Printf("stack: %s%s\n", dots, list2str(last))
+	}
 }
 
 // Execute a math function, check if it is defined just in case